Department of Animal Science, Federal University of Viçosa, Viçosa, Minas Gerais, Brazil.
Department of Animal Science, Federal University of Bahia, Salvador, Bahia, Brazil.
J Anim Sci. 2018 Mar 6;96(2):670-683. doi: 10.1093/jas/sky018.
The objective of this study was to determine the apparent and true intestinal digestibility of total and individual AA, and to estimate the efficiency of whole-body AA retention from individual and total absorbed AA. Four Nellore animals (241.3 kg initial BW) and four crossbred Angus × Nellore (263.4 kg initial BW) cannulated in rumen and ileum were randomly allocated in two 4 × 4 Latin squares. The experiment lasted four 17 d periods, with 10 d for adaptation to diets and another 7 d for data collection. The diets consisted of increasing CP levels: 100, 120, or 140 g/kg of DM offered ad libitum, and restricted intake diet with 120 g CP/kg DM (experiment 1). In experiment 2, forty-four bulls (22 Nellore and 22 crossbred F1 Angus × Nellore) with 8 months and initial shrunk BW 215.0 ± 15.0 kg (Nellore = 208.0 ± 12.78 kg; Angus × Nellore = 221.9 ± 14.16 kg) were used. Eight of those animals were slaughtered at the beginning of the experiment. The remaining 36 bulls were allocated in a completely randomized design with six replicates, in a 2 (genetic groups) × 3 (CP contents) factorial scheme. The amount of essential AA (EAA) and nonessential AA (NEAA) reaching the small intestine increased linearly (P < 0.05) in response to CP content. The apparent digestibility of EAA was not affected (P > 0.05) by CP content, with exception for histidine (P = 0.07, linear effect), leucine (P = 0.01, linear effect), and methionine (P = 0.05, linear effect). Differences existed among AA when compared the apparent digestibility of NEAA. The apparent digestibility of alanine (P = 0.05), aspartic acid (P = 0.07), glutamic acid (P = 0.02), glycine (P = 0.05), proline (P = 0.02), and serine (P = 0.04) responded quadratically to CP content increase. However, the apparent digestibility of cystine and tyrosine was not affected (P > 0.05) by increasing dietary CP. The true intestinal digestibilities of total, essential, nonessential AA, lysine, and methionine were 75.0%, 77.0%, 74.0%, 77.0%, and 86%, respectively. The true intestinal digestibility of total microbial AA was 80%. The efficiency of utilization of total AA for whole-body protein deposition was 40%. The efficiency of utilization of lysine and methionine was 37% and 58%, respectively. It was concluded that the AA flow to the omasum increases in response to dietary CP content. In addition, there are differences among AA in the efficiency that they are used by beef cattle.
本研究旨在确定总氨基酸和各氨基酸的表观和真消化率，并估计从总吸收氨基酸和各氨基酸估计全身氨基酸保留的效率。4 头（初始体重 241.3kg）和 4 头（初始体重 263.4kg）瘤胃和回肠有瘘管的安格斯×尼洛牛杂种牛随机分配在 2 个 4×4 拉丁方中。试验持续 4 个 17d 期，适应期 10d，收集数据期 7d。日粮由逐渐增加的 CP 水平组成：自由采食的 100、120 或 140g/kg 干物质，以及限制摄入的 120g CP/kg DM 日粮（试验 1）。在试验 2 中，44 头公牛（22 头尼洛牛和 22 头安格斯×尼洛牛杂种牛），月龄 8 个月，初始去脂活重 215.0±15.0kg（尼洛牛=208.0±12.78kg；安格斯×尼洛牛=221.9±14.16kg）被使用。其中 8 头动物在试验开始时被屠宰。剩余的 36 头公牛被完全随机设计，6 个重复，2（遗传组）×3（CP 含量）因子方案分配。到达小肠的必需氨基酸（EAA）和非必需氨基酸（NEAA）的量随 CP 含量线性增加（P＜0.05）。CP 含量对 EAA 的表观消化率没有影响（P＞0.05），除了组氨酸（P=0.07，线性效应）、亮氨酸（P=0.01，线性效应）和蛋氨酸（P=0.05，线性效应）。当比较 NEAA 的表观消化率时，AA 之间存在差异。丙氨酸（P=0.05）、天冬氨酸（P=0.07）、谷氨酸（P=0.02）、甘氨酸（P=0.05）、脯氨酸（P=0.02）和丝氨酸（P=0.04）的表观消化率随 CP 含量的增加呈二次曲线变化。然而，胱氨酸和酪氨酸的表观消化率不受日粮 CP 增加的影响（P＞0.05）。总、必需、非必需氨基酸、赖氨酸和蛋氨酸的真肠道消化率分别为 75.0%、77.0%、74.0%、77.0%和 86%。总微生物 AA 的真肠道消化率为 80%。全身蛋白质沉积的总氨基酸利用率为 40%。赖氨酸和蛋氨酸的利用率分别为 37%和 58%。结论是，AA 向瘤胃的流量随日粮 CP 含量而增加。此外，牛对 AA 的利用效率存在差异。
